The present invention relates to an ignition system in which an ignition distributor containing a rotation signal generator is integrated with an ignition coil and an ignition amplifier, or more in particular to such a system which is prevented from an erroneous operation or malfunction which otherwise might be caused by magnetic fluxes leaking from the ignition coil.
An ignition system generally used in an internal combustion engine is shown in FIG. 1. A signal rotor 1 having as many protrusions as the cylinders of the internal combustion engine E is rotated in synchronisum with the rotation of the engine E. The signal rotor 1 is opposed to an electromagnetic pickup 2 including a pickup coil 21 having an axis thereof in radial direction of the signal rotor and a permanent magnet 22. With the rotation of the signal rotor 1, magnetic fluxes change so that an output signal (rotation signal) is generated in synchronism with the engine rotation in the coil 21 of the pickup 2. In accordance with the output signal of this electromagnetic pickup 2, an ignition amplifier 3 controls an intermittent current flow through the primary winding 41 of the ignition coil 4 by a battery 5.
Assume that the signal rotor 1 rotates from the position where one of the protrusions thereof is opposed to the pickup 2 to the position where the next protrusion is opposed to the pickup 2. The magnetic flux produced from the permanent magnet 22 and linking the pickup coil 21 change, and an output signal voltage of a waveform shown by solid line in FIG. 2(a) is generated in the pickup coil 21. The ignition amplifier 3 controls the current supply at a predetermined detection level V.sub.0 shown by dashed line on the basis of this output signal waveform, so as to supply a current to the primary winding 41 of the ignition coil 4 when the signal voltage is positive as compared with the detection level V.sub.0 and to cut off current supply to the primary winding 41 when the signal voltage is negative. In this way, the current flowing in the primary winding 41 of the ignition coil 4 is controlled as shown in FIG. 2(b). The ordinate of FIGS. 2(a) and 2(b) represents the voltage V and the current i respectively, and the abscissa thereof represents time t.
When current supply to the primary winding 41 of the ignition coil 4 is cut off, a high voltage is induced across the secondary winding 42. This high voltage is applied to a spark plug 7 of each cylinder of the engine E through distribution made by a distributor 6. The engine E is thus ignited.
In this ignition system, the signal rotor 1 is mounted on a rotary shaft of the distributor 6 and the electromagnetic pickup 2 is arranged in the distributor 6 in opposed relation thereto. In addition, it has been suggested in recent years that the ignition coil 4 and the ignition amplifier 3 are both integrated with the distributor 6 primarily for the purpose of improving the mountability thereof on the vehicle and the reliability of connecting means, as well known.
If the ignition coil is integrated with the distributor, however, an erroneous signal is liable to be generated from the electromagnetic pickup making up a rotation signal generator by the magnetic flux leaking from the ignition coil. The problem is how to overcome this difficulty.
An explanation will be made with reference to an ignition coil of closed magnetic loop type generally used as the ignition coil 4, in which a pair of E-shaped iron cores 43 and 43' are arranged in opposition to each other and include central legs wound with the primary and secondary windings 41 and 42 as shown in FIG. 3 in principle. In the case of this ignition coil, current supply to the primary winding 41 causes main magnetic flux whose axis A posses through the central legs 43a and 43'a of the E-shaped iron cores 43 and 43'. Even in this ignition coil 4 of closed magnetic loop type, as is well known, there is a leakage magnetic flux from the magnetic circuit. This leakage magnetic flux .0..sub.L is generated radially from the substantial center of the E-shaped core 43 and is converged at the substantial center of the opposite E-shaped core 43'.
If this ignition coil, together with the electromagnetic pickup, is integrated with the distributor, the coil of the electromagnetic pickup is inevitably arranged so as to be linked with the leakage magnetic flux, with a natural result that a noise voltage attributable to the leakage magnetic flux is generated in the coil of the electromagnetic pickup.
Let us now consider the effect of the leakage magnetic flux on the assumption that the coil 21 of the electromagnetic pickup and the ignition coil 4 are arranged as shown in FIG. 4a. FIGS. 4a and 4b are sectional views of the ignition coil 4 taken along the main magnetic flux axis A attributable to the primary winding current. The pickup coil 21 has a magnetic flux sensibility in the direction X, while the leakage magnetic flux .0..sub.L of the ignition coil 4 is directed from the upper end to the lower end of the main magnetic flux path.
As shown, the pickup coil 21 is arranged substantially midway of the magnetic path of the main magnetic flux axis A of the ignition coil 4 so that the magnetic flux sensitive direction X crosses the main magnetic flux axis A of the ignition coil 4 at right angles. In this case, the leakage magnetic flux .0..sub.L links the magnetic flux sensitive direction X of the pickup coil 21 substantially at right angles, and any noise voltage is not superimposed.
Actually, however, it is well known that it is difficult to form such a uniform magnetic field by the leakage magnetic flux as shown in FIG. 4a. As shown in FIG. 4b, for instance, a distribution shaft 150 and the signal rotor 1 are generally inserted between the coil 21 of the electromagnetic pickup and the ignition coil 4 as described later. In this case, even though the pickup coil 21 is arranged substantially midway of the magnetic path of the main magnetic flux axis A of the ignition coil with the magnetic flux sensitive direction X crossing the main magnetic flux axis A of the ignition coil 4 in a direction perpendicular thereto, the distribution shaft 150 and the signal rotor 1 are presented as magnetic materials between the pickup coil 21 and the ignition coil 4 and hence the route of the leakage magnetic flux changes, resulting in that part of the leakage flux undesirably links the pickup coil 21. Therefore, a noise voltage caused by the leakage magnetic flux .0..sub.L is thus superimposed on the output of the pickup coil 21, thereby causing an erroneous operation of the ignition amplifier 3.